Filtration equipment with filtrate recovery process

ABSTRACT

In a filtration equipment with a filtrate recovery process, in order to achieve reduction in recovery time of suspension in a tank and allow sludge such as filtration aid to be exfoliated readily from filtration elements and discharged, pressurized water is introduced into the tank which includes tubular filtration elements and a plate element provided at upper and lower locations thereof to recover the suspension as filtrate, and pressurized gas such as air or carbon dioxide is introduced into the tank from the suspension side so that water remaining on the suspension side is discharged from the tank by the pressurized gas, whereafter sludge is exfoliated from the filtration elements and then discharged to the outside of the tank.

FIELD OF THE INVENTION

This invention relates to filtration equipment for clarifying foodproducts such as beer or sake or for clarifying chemical products suchas flocculants or paper coating agents, and more particularly tofiltration equipment with a filtrate recovery apparatus.

BACKGROUND OF THE INVENTION

Conventionally, as filtration equipment of the type described,filtration equipment of the suspended filtration element type andfiltration equipment of the upright filtration element type are known.

First, a conventional filtration equipment of the suspended element typeis described with reference to FIG. 10. FIG. 10 is a partial sectionalview of a conventional filtration equipment of the suspended elementtype.

As shown in FIG. 10, a filtration equipment of the type describedincludes an upper tank 101a and a lower tank 101b partitioned and sealedfrom each other by a partition plate 103. A plurality of tubularfiltration elements 102 made of a ceramics material and each closed atthe lower end thereof are provided in a suspended condition on thepartition plate 103.

Suspension to be filtered is supplied into the lower tank 101b by a pump110 and is filtered by the tubes of the filtration elements 102,whereafter it is collected into the upper tank 101a through hollowportions. The filtrate filtered and collected into the upper tank 101aisdelivered to a filtrate storage tank (not shown). Filter aid isprecoated on the surface of each of the filtration elements 102 so thatchoking of the filtration elements 102 is prevented to maintain astabilized filtration capacity.

A conventional filtration equipment of the upright filtration elementtype is described with reference to FIG. 11. FIG. 11 is a sectional viewof a conventional filtration equipment of the upright element type.

As shown in FIG. 11, a filtration equipment 121 of the type mentionedincludes a delivery pipe 125 provided at a lower portion of a tank 121aand connected to a filtrate storage tank (not shown), and a plurality oftubular filtration elements 122 are provided uprightly on a deliverypipe 125. Hollow portions of the filtration elements 122 and a hollowportion of the delivery pipe 125 are communicated with each other sothat the suspension supplied to the tank 121a passes through and isfiltered by the filtration elements 122 and then delivered to thefiltrate storage tank through the delivery pipe 125. It is to be notedthat, also with the filtration equipment 121 of the upright elementtype, filter aid is precoated on the surfaces of the filtration elements122 in order to maintain a stabilized filtration capacity.

By the way, whether the filtration equipment is of the suspended elementtype or of the upright element type described above, although filter aidis precoated on the surfaces of the filtration elements, if filteredsubstances adhere to and are deposited in a large amount on the surfacesof the filtration elements, then the filtration capacity of thefiltration equipment is deteriorated. Therefore, the filtered substancesdeposited on the surfaces of the filtration elements must be removed bywashing in accordance with necessity. In this instance, the filtrationoperation is interrupted once and the suspension remaining in the tankis processed, and then the filtration elements are washed individually.

For the processing of the suspension remaining in the tank, it wouldseem possible to recover the full amount of the suspension from the tankand then resume filtration processing after the filtration elements arewashed. However, since filtered substances deposited on the surfaces ofthe filtration elements merely adhere to the surfaces of the filtrationelements by a pressure difference caused by flows of the liquid from thesuspension side (primary side) to the filtrate side (secondary side),there is the possibility that, upon recovery, the filtered substances(including the filter aid) deposited on the surfaces of the filtrationelements may exfoliate and mix into the suspension. Further, infiltration of, for example, beer, when it is tried to produce adifferent product of beer having a different quality by the sameprocess, the beer cannot be returned to a preceding step to performfiltration again. Accordingly, upon changing over to a product of adifferent quality, the remaining suspension must be recovered at thepreceding step.

Therefore, it is a conventional practice to supply water gently into atank from a lower portion to recover suspension such as beer beingfiltered to the secondary side in such a manner that the suspensionbeing filtered and the water are not mixed with each other as far aspossible (hereinafter referred to as "water drive") or in order toprocess suspension in a condition in which the pressure differencebetween the primary side and the secondary side is maintained, byintroducing pressurized air or pressurized gas such as carbon dioxideinto the tank to filter the remaining suspension with the pressure ofthe pressurized air and then recover the thus filtered suspension.

DISCLOSURE OF THE INVENTION

However, where the water drive is employed, even if water is suppliedvery gently, the water is mixed into the suspension, and as a result,filtrate diluted with water is recovered. Consequently, the recoveredfiltrate cannot be used as a product. Even if careful water drive isperformed to recover the filtrate in such a manner that the suspensionbeing filtered and the water are not mixed with each other, if the levelof the water reaches the filtration elements, then the water is mixedinto the filtrate. Consequently, the filtrate since then cannot be usedas a product, resulting in much waste.

Further, when pressurized gas is supplied into the tank to process theremaining suspension, if the suspension in the tank has a levelsufficient to reach the filtration elements, then the suspension can befiltered and recovered. However, if the level becomes lower than thefiltration elements, then the suspension can no longer be filtered orrecovered, and some always remains non-recovered. Particularly where thefiltration equipment is of the suspended element type, if the leveldrops until upper portions of the filtration elements are exposed, thenthe pressurized gas will flow into a delivery route of the filtratethrough the filtration elements, substantially resulting in failure infiltration and recovery.

Accordingly, it is an object of the present invention to provide afiltration equipment with a filtrate recovery process which can filterand recover all suspension in a tank in a short time.

In order to attain the object described above, according to the presentinvention, a filtration equipment with a filtrate recovery process ischaracterized in that it comprises a tank to which suspension issupplied, tubular filtration elements provided in the tank for filteringthe suspension, delivery means for delivering the filtrate filtered bythe tubular filtration elements to the outside of the tank, a platefiltration element located below the tubular filtration elements in theinside of the tank for maintaining the airtightness of the space inwhich the tubular filtration elements are provided, second deliverymeans for delivering the filtrate filtered by the plate filtrationelement to the outside of the tank, and pressurized gas introductionmeans for introducing pressurized gas into the tank when the suspensionin the tank is recovered.

Another filtration equipment with a filtrate recovery apparatus ischaracterized in that it comprises a tank to which suspension beforefiltration is supplied, tubular filtration elements provided in the tankfor filtering the suspension, delivery means for delivering the filtratefiltered by the tubular filtration elements to the outside of the tank,a plate filtration element located below the tubular filtration elementsin the inside of the tank for maintaining the airtightness of the spacein which the tubular filtration elements are provided, second deliverymeans for delivering the filtrate filtered by the plate filtrationelement to the outside of the tank, pressurized liquid introductionmeans for introducing pressurized liquid into the tank when thesuspension in the tank is recovered, and pressurized gas introductionmeans for introducing pressurized gas into the tank in order todischarge the pressurized liquid, to the outside of the tank.

Each of the filtration equipments is further characterized in that thesuspension in the tank is filtered simultaneously by the tubularfiltration element and the plate filtration element, or/and that theplate filtration element is installed in a manner that it can beinclined with respect to a horizontal plane.

In any of the filtration equipments with a filtrate recovery process ofthe present invention, since the tubular filtration elements and theplate filtration element are provided in the inside of the tank,filtration of suspension in the tank is performed by both filtrationelements, and the filtrate is delivered to the outside of the tank bytheir respective delivery means.

When the suspension in the tank is to be recovered such as when thefiltration elements are to be washed, pressurized gas is introduced intothe inside of the tank by the pressurized gas introduction means so thatthe suspension remaining in the tank is delivered by the pressure of thepressurized gas and recovered. In this instance, although filtration isperformed by both filtration elements and the filtrate is recovered,after the level of the suspension in the tank becomes lower than a fixedlevel, filtration by the tubular filtration elements becomes impossible.However, since the plate filtration element is provided below thetubular filtration elements so that the airtightness of the space inwhich the tubular filtration elements is provided may be kept, theremaining suspension is filtered by the plate filtration element andrecovered.

In a filtration equipment with a filtrate recovery process whichincludes filtration elements with a siphon pipe suspended at an upperportion of a tank and a rotational plate filtration element provided ata lower portion of the tank, pressurized water is introduced into thetank through an upper portion to recover suspension as filtrate, andthen gas such as air or carbon dioxide is pressurized from an upperportion of the suspension side to discharge the water remaining on thesuspension side through an outlet port provided at a lower portion ofthe tank. Thereafter water is expelled from sludge adhering to thefiltration elements by the pressurized gas and the lower platefiltration element is opened to remove the sludge from the filtrationelements and discharge it as dry sludge.

Further, where filter aid is precoated on the surfaces of the filtrationelements in order to maintain a stabilized filtration capacity, ifsolution is not flowing from the primary side (suspension side) to thesecondary side (filtrate side) of the filtration elements, the precoatlayers exfoliate. Therefore, by performing filtration by both thetubular filtration elements and the plate filtration element, theprecoat layers on the filtration elements does not exfoliate duringfiltration.

Furthermore, where the plate filtration element is installed so that itcan be inclined with respect to the horizontal plane, filteredsubstances deposited on the plate filtration element drop by their ownweight when the plate filtration element is pivoted and are removed fromthe plate filtration element.

As described above, according to the present invention, since thefiltration equipment includes the plate filtration element providedbelow the tubular filtration elements and the second delivery means fordelivering the filtrate filtered by the plate filtration element to theoutside of the tank, the suspension in the tank is recovered, all thesuspension remaining in the tank can all be filtered and recovered.

Further, by filtering the suspension in the tank simultaneously by thetubular filtration elements and the plate filtration element, wherefilter aid is precoated on the surfaces of the filtration elements,exfoliation of the precoat layers during filtration can be prevented.

Furthermore, by installing the plate filtration element so that it canbe inclined with respect to the horizontal plane, mere inclination ofthe plate filtration element can readily remove filtered substancesdeposited on the plate filtration element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a filtration system employing a firstembodiment of the filtration equipment of the present invention;

FIG. 2 is a sectional view showing a construction of a second embodimentof the filtration equipment of the present invention;

FIG. 3 is a sectional view of the filtration equipment shown in FIG. 2as viewed in the direction indicated by arrow mark A;

FIG. 4 is a sectional view showing an example of a support structure ofa filtrate recovery vessel on a tank of the filtration equipment shownin FIG. 2;

FIG. 5 is a sectional view showing an example of a connection structureof the filtrate recovery vessel to a second delivery pipe of thefiltration equipment shown in FIG. 2;

FIGS. 6a and 6b are a view illustrating a washing step of the platefiltration element of the filtration equipment shown in FIG. 2;

FIG. 7 is a sectional view showing a third embodiment of the filtrationequipment of the present invention;

FIG. 8 is a sectional view of a tubular filtration element with a siphonpipe of a fourth embodiment of the of the filtration equipment of thepresent invention;

FIG. 9 is a sectional view showing a construction of a fifth embodimentof the filtration equipment of the present invention;

FIG. 10 is a partial sectional view of a conventional filtrationequipment of the suspended element type; and

FIG. 11 is a sectional view of a conventional filtration equipment ofthe upright element type.

BEST FORMS IN EMBODYING THE INVENTION

Embodiments of the present invention are described below with referenceto the drawings.

(First Embodiment )

FIG. 1 is a schematic view of a filtration system which employs a firstembodiment of the filtration equipment of the present invention. Asshown in FIG. 1, the filtration equipment 1 of the present embodiment isthe filtration equipment 1 of the upright element type, and a firstdelivery pipe 5a serving as delivery means connected to a filtratestorage tank (not shown) is provided in a tank 1a such that it extendsthrough a side wall of the tank 1a. In the inside of the tank 1a, aplurality of tubular filtration elements 2 are provided uprightly on thefirst delivery pipe 5a, and hollow portions of the tubular filtrationelements 2 and a hollow portion of the first delivery pipe 5a arecommunicated with each other. For the tubular filtration elements 2, aknown cylindrical filter made of a ceramics material, a porouscylindrical filter made of a sintered metal, a filter of the windingtype wherein a wire is wound in a coil on a cylindrical member andfiltration is performed through gaps of the wire or some other filter isused.

Further, at the bottom of the tank 1a, a filtrate collection vessel 3connected to a second delivery pipe 5b, which serves as second deliverymeans, via a valve 11k is secured. A plate filtration element 4 ismounted on the top face of the filtrate collection vessel 3. A packing(not shown) is provided over the entire circumference of the vesselalong the outer peripheral edge of the plate filtration element 4, andthe airtightness of the space in the inside of the tank 1a in which thetubular filtration elements 2 are provided is maintained by the packing.Airtightness is necessary to prevent leakage of the suspension suppliedinto the tank 1a from above the plate filtration element 4 to a locationbelow the plate filtration element 4. For the plate filtration element4, a filter made of a ceramics material, a porous filter made of asintered metal or some other filter is used. Meanwhile, a dischargingpipe 12 for discharging cleansing solution therethrough upon washing ofthe tubular filtration elements 2 is connected to the filtratecollection vessel 3 via a valve 11d.

The second delivery pipe 5b joins to an intermediate portion of thefirst delivery pipe 5a, and a valve 11h is provided on the downstreamside of the first delivery pipe 5a with respect to the joining portionof the first delivery pipe 5a to the second delivery pipe 5b.Consequently, the second delivery pipe 5b is connected to the filtratestorage tank via the first delivery pipe 5a.

A suspension supply pipe 6 is connected to a portion of the tank 1aabove the plate filtration element 4 via a valve 11c. A pump 10 isprovided for the suspension supply pipe 6, and by changing over valves11a and 11b, the suspension stored in a suspension tank (not shown) orprecoating solution stored in a precoat tank 9 is supplied into tank 1a.The precoating solution contains filter aid to be precoated on thesurfaces of the tubular filtration elements 2 and the plate filtrationelement 4 prior to filtration of the suspension. For the filter aid,diatomaceous earth, perlite, cellulose or some other substance is used.

A gas introduction pipe 7 serving as pressurized gas introduction meansfor introducing pressurized air or pressurized gas such as carbondioxide into the inside of the tank 1a is connected to an upper portionof the tank 1a, and a valve 11f is provided for the gas introductionpipe 7.

A precoating solution feedback pipe 8 is provided to return precoatingsolution supplied to the filtration equipment 1 into the precoat tank 9,and is connected to the upstream side of the first delivery pipe 5a withrespect to the valve 11h and provided with a valve 11j.

It is to be noted that, while a filter made of a porous material such asa ceramics material or a sintered metal, or a filter of the winding type(tubular filtration element) or a filter cloth (both utilized for aplate filtration element) can be used as a material for the tubularfiltration elements 2 and the plate filtration element 4, since theelements may possibly be corrode depending upon the properties of thesuspension (acid, the alkali, high temperature and so forth), an optimummaterial is used as the material of the elements depending on theproperties of the suspension.

Next, operation of the filtration system of the present embodiment isdescribed.

First, precoating processing which is performed prior to filtration ofthe suspension is described. When precoating, the valves 11b, 11c, 11kand 11j are opened, and the pump 10 is started to circulate precoatingsolution from the precoat tank 9 through the suspension supply pipe6→filtration equipment 1→first delivery pipe 5a, second delivery pipe5b→precoating solution feedback pipe 8→precoat tank 9. Consequently, aprecoat layer is formed on the surfaces of the tubular filtrationelements 2 and the surface of the plate filtration element 4.

Next, the filtering operation is described. The valves 11a, 11c, 11h and11k are opened and the pump 10 is started. Consequently, the suspensionin the suspension tank is supplied into the tank 1a through thesuspension supply pipe 6, and is filtered by the tubular filtrationelements 2 and the plate filtration element 4. The filtrate filtered bythe tubular filtration elements 2 is delivered to the filtrate storagetank through the first delivery pipe 5a. Meanwhile, the filtratefiltered by the plate filtration element 4 is collected into thefiltrate collection vessel 3 and delivered to the filtrate storage tankthrough the second delivery pipe 5b.

Here, while filtration is performed simultaneously by both of thetubular filtration elements 2 and the plate filtration element 4, it isalso possible to close valve valve 11k to perform filtration only by thetubular filtration elements 2. However, unless the solution is flowing,during filtration, from the primary side (suspension side) to thesecondary side (filtrate side), that is, unless the precoat layersremain pressed against the surfaces of the filtration elements, theprecoat layers are liable to be exfoliate, and therefore, the tubularfiltration elements 2 must always be kept in a filtering condition.Further, by performing filtration by the tubular filtration elements 2and the plate filtration element 4, the filtration processing rate isincreased and also the filtration efficiency is improved.

If filtration is performed for a long period of time, then filteredsubstances adhere to and are deposited on the surfaces of the tubularfiltration elements 2 and the surface of the plate filtration element 4.Since the filtration capacity is deteriorated if filtered substances aredeposited on the surfaces of the tubular filtration elements 2 and thesurface of the plate filtration element 4, the tubular filtrationelements 2 and the plate filtration element 4 are washed when necessary.In this case, the process of recovering the suspension from the tank 1ais performed.

In the following, the suspension recovery process is described.

When suspension processing is performed, the valve 11f of the gasintroduction pipe 7 is first opened, and then the valves 11a and 11c areclosed. Consequently, pressurized gas is introduced into the tank 1a.Under the pressure of the pressurized gas, the suspension remaining inthe tank 1a is filtered by the tubular filtration elements 2 and theplate filtration element 4 and recovered into the filtrate storage tank.

If the suspension in the tank 1a is decreased by the suspensionprocessing until the level of the suspension becomes lower than thelower ends of the tubular filtration elements 2, then filtration by thetubular filtration elements 2 is stopped. However, since the precoatlayers and filtered substances are pressed against the surfaces of thetubular filtration elements 2 by the pressurizing gas, the precoatlayers and the filtered substances do not exfoliate and filtration bythe plate filtration element 4 continues. Consequently, the suspensionin the tank 1a can all be filtered and recovered.

After the suspension in the tank 1a is recovered, the valve 11d isopened and then the valve 11k is closed, whereafter the cleansingsolution is flowed reversely from the first delivery pipe 5a to the tank1a to wash away the filtered substances deposited on the surfaces of thetubular filtration elements 2. The filtered substances washed away bythe cleansing solution drop onto the plate filtration element 4 whilethe cleansing solution is collected into the filtrate collection vessel3. The cleansing solution is discharged from the discharging pipe 12 viathe valve 11d.

Meanwhile, filtered substances adhering as a result of the filtration tothe surface of the plate filtration element 4 and the filteredsubstances dropping from the tubular filtration elements 2 by washing ofthe tubular filtration elements 2 are deposited on the surface of theplate filtration element 4. In order to wash the plate filtrationelement 4 on which the filtered substances are deposited, for example,an output port (not shown) for the plate filtration element 4 is formedin the tank 1a so that the plate filtration element 4 can be taken outthrough the output port and washed. It is a matter of course that theoutput port must have a sealed structure so that leakage of thesuspension through the tank 1a may be prevented during filtration.

Since also the precoat layers come off if washing of the tubularfiltration elements 2 and the plate filtration element 4 is performed,precoating processing is performed again after the tubular filtrationelements 2 and the plate filtration element 4 are washed.

While an example wherein the filtrate collection vessel 3 on which theplate filtration element 4 is mounted is provided in the inside of thetank 1a is described in the present embodiment, the filtrate collectionvessel 3 may be provided such that the plate filtration element 4 servesas the bottom wall of the tank 1a itself.

It is to be noted that, if, at a point in time when recovery of thesuspension is completed, the deposited filtered substances on thesurfaces of the filtration elements 2 and 4 are so small in amount thatthe filtering function can be exhibited sufficiently, then the washingstep described above is not performed, but the valves 11a, 11c, 11h and11k are opened to supply the suspension to be filtered into the tank 1a.After the tank 1a is filled with the suspension and a filteringoperation is started, the valve 11f is closed to stop the introductionof the gas which presses the precoat layers so that they do notexfoliate.

(Second Embodiment)

FIG. 2 is a sectional view showing a construction of a second embodimentof a filtration equipment of the present invention, and FIG. 3 is asectional view of the filtration equipment shown in FIG. 2 as viewed inthe direction of an arrow mark A.

The filtration equipment 21 of the present embodiment is different fromthe first embodiment in two points described below.

(1) A filtrate collection vessel 23 is supported for pivotal motionaround a shaft 23a extending in a horizontal direction. In particular,the filtrate collection vessel 23 is supported for pivotal motion in thedirection indicated by an arrow mark B in FIG. 3. A plate filtrationelement 24 similar to that in the first embodiment is provided on thetop face of the filtrate collection vessel 23. A packing 23b is providedon an outer peripheral edge of the plate filtration element 24, and theairtightness of the space in the filtration equipment 21 in whichtubular filtration elements 22 are provided is kept by the packing. Inorder to support the shaft 23a of the filtrate collection vessel 23, forexample, as shown in FIG. 4, roller bearings 34 are provided on a tank21a, and the shaft 23a of the filtrate collection vessel 23 is fitted inthe inner races of the roller bearings 34 to support the shaft 23a forrotation.

(2) As the filtrate collection vessel 23 is supported for pivotalmotion, the filtrate collection vessel 23 is connected for pivotalmotion also to a second delivery pipe 25b. In order to connect thefiltrate collection vessel 23 and the second delivery pipe 25b to eachother, for example, as shown in FIG. 5, a roller bearing 35 is providedon the inner periphery of the second delivery pipe 25b and an endportion of the shaft 23a of the filtrate collection vessel 23 is fittedin the inner race of the roller bearing 35 to support the shaft 23a forrotation. Further, in order to prevent leakage of suspension from theconnection location between the shaft 23a of the filtrate collectionvessel 23 and the second connection pipe 25b, a packing 36 is providedbetween the shaft 23a and the second delivery pipe 25b.

Since the other construction is similar to that of the first embodiment,description of it is omitted here.

By providing the filtrate collection vessel 23 for pivotal motion inthis manner, washing of the plate filtration element 24 provided on theupper face of the filtrate collection vessel 23 is facilitated. In thefollowing, the washing step of the plate filtration element 24 in thepresent embodiment is described.

When recovery of the suspension in the tank 21a is completed, a filteredsubstance 39 remains deposited on the top face of the plate filtrationelement 24 as seen in (a) of FIG. 6. Thus, if the filtrate collectionvessel 23 is pivoted to incline the plate filtration element 24 withrespect to a horizontal plane as seen in (b) of FIG. 6, then thefiltered substance 39 drops from the plate filtration element 24. Thepivotal motion of the filtrate collection vessel 23 may be performed bya rotational driving mechanism (not shown) which makes use of a motor ormay be performed manually.

Thereafter, cleaning water is flowed reversely from a first deliverypipe 25a to wash the tubular filtration elements 22. In this instance,if also a valve 31k of the second delivery pipe 25b is open, then thecleaning water flows reversely also from the second delivery pipe 25b,and also the plate filtration element 24 can be washed. Then, thefiltered substance 39 is discharged to the outside of the tank togetherwith the cleaning water. After the washing of the tubular filtrationelements 22 and the plate filtration element 24 is completed, thefiltrate collection vessel 23 is moved back to its original position.

As described above, by providing the filtrate collection vessel 23 forpivotal motion, the filtered substance 39 deposited on the platefiltration element 24 can be discharged to the outside of the tank, andsince washing with cleansing solution can be performed in thiscondition, washing of the plate filtration element 24 is simplified. Itis to be noted that, when the filtered substance 39 deposited on theplate filtration element 24 can be exfoliated sufficiently only bycausing the filtered substance 39 to be dropped, then washing withcleansing solution need not necessarily be performed. Further, washingof the tubular filtration elements 22 and washing of the platefiltration element 24 may be performed simultaneously or separately fromeach other. However, when washing of the tubular filtration elements 22and washing of the plate filtration element 24 are performed separatelyfrom each other, washing of the tubular filtration elements 22 must beperformed first since filtered substances adhering to the tubularfiltration elements 22 drop onto the plate filtration element 24 bywashing of the tubular filtration elements 22.

(Third Embodiment)

FIG. 7 is a sectional view showing a construction of a third embodimentof the filtration equipment of the present invention.

The present embodiment is the filtration equipment 41 of the elementsuspending type and includes an upper tank 41a and a lower tank 41bpartitioned and sealed from each other by a partition plate 53. Theupper tank 41a and the lower tank 41b are secured by means of bolts andnuts similarly as in the structure shown in FIG. 10. A plurality oftubular filtration elements 42 similar to those of the first embodimentsuspend from the partition plate 53.

A first delivery pipe 45a for delivering filtrate filtered by thetubular filtration elements 42 to a filtrate storage tank (not shown) isconnected to the upper tank 41a. The first delivery pipe 45a ispreferably provided in the proximity of the bottom face of the uppertank 41a, that is, the depth position at which the partition plate 53 isprovided. This is so that as much as possible if the filtrate filteredby the tubular filtration elements 42 and arriving at the upper tank 41acan be delivered to the filtrate storage tank. The most preferable formis to provide, in the inside of the partition plate 53, delivery means(liquid flow path) interconnecting the top ends of the tubularfiltration elements 42 and the first delivery pipe 45a.

Meanwhile, a filtrate collection vessel 43 is provided for pivotalmotion on the lower tank 41b in a similar manner as in the secondembodiment. A plate filtration element 44 similar to that of the firstembodiment is provided on the top face of the filtrate collection vessel43. A packing is provided on the outer peripheral edge of the platefiltration element 44, and the airtightness of the space in the lowertank 41b in which the tubular filtration elements 42 is provided is keptby the packing. A second delivery pipe 45b for delivering filtratefiltered by the plate filtration element 44 to the filtrate storage tankis connected to the filtrate collection vessel 43 via a rotary joint 54.The rotary joint 54 may have a construction similar to that shown inFIG. 5, and by means of the rotary joint 54, the filtrate collectionvessel 43 is supported for pivotal motion so that it can be inclinedwith respect to the second delivery pipe 45b.

Further, a gas introduction pipe 47 for introducing pressurized gasduring processing of suspension is connected to the lower tank 41b, andthe bottom of the lower tank 41b is opened so that filtered substancesby the tubular filtration elements 42 and the plate filtration element44 and cleansing solution can be discharged to the outside therethrough.A suspension supply pipe 46 is connected to a location at the lower tank41b above the plate filtration element 44.

It is to be noted that, since the construction of the entire filtrationsystem may be the same as that of the first embodiment, descriptionthereof is omitted here.

With the construction described above, during filtration, suspension issupplied through the suspension supply pipe 46 to the lower tank 41b.The suspension is filtered by the tubular filtration elements 42 and theplate filtration element 44. The filtrate filtered by the tubularfiltration elements 42 is collected into the upper tank 41a and thendelivered to the filtrate storage tank through the first delivery pipe45a. The filtrate filtered by the plate filtration element 44 iscollected into the filtrate collection vessel 43 and then delivered tothe filtrate storage tank through the second delivery pipe 45b. Althoughthe filtration of the suspension can be performed only by the tubularfiltration elements 42, preferably it is performed by both of thetubular filtration elements 42 and the plate filtration element 44 forthe same reason as that of the first embodiment.

Meanwhile, during recovery processing of the suspension in thefiltration equipment 41, the gas introduction pipe 47 is opened tointroduce pressurized gas into the lower tank 41b, and then the supplyof the suspension into lower tank 41b is stopped. Under the pressure ofthe pressurized gas, the suspension remaining in the lower tank 41b isfiltered by the tubular filtration elements 42 and the plate filtrationelement 44 and recovered. After the suspension in the lower tank 41bdecreases in amount as a result of the recovery until the filtrationfaces of the tubular filtration elements 42 are exposed, the pressurizedgas flows through the exposed portions of the filtration faces to thefiltrate side and the filtration by the tubular filtration elements 42is no longer performed. However, since the filtration by the platefiltration element 44 continues, the suspension in the filtrationequipment 41 can be filtered fully and recovered. Moreover, sincefiltration can be performed by the plate filtration element 44 evenafter filtration by the tubular filtration elements 42 becomesimpossible, even if the pressure of the pressurized gas to be introducedinto the lower tank 4lb is raised higher than 0.1 to 0.2 kgf/cm², thereis no problem and recovery of the suspension remaining in the lower tank41b can be performed efficiently.

Since washing of the tubular filtration elements 42 and the platefiltration element 44 after the recovery of the suspension in thefiltration equipment 41 is similar to that in the second embodiment,description of it is omitted here.

(Fourth Embodiment)

FIG. 8 is a sectional view of a filtration element with a siphon pipe ofa fourth embodiment of the filtration equipment of the presentinvention. While, in the third embodiment, a known tubular filter isused for the tubular filtration elements, in the present embodiment, atubular filtration element 62 with a siphon pipe which is an improvementof the tubular filter is employed. Since the construction except thetubular filtration element 62 with a siphon pipe is similar to that ofthe third embodiment, the tubular filtration element 62 with a siphonpipe employed in the present embodiment is described below.

The tubular filtration element 62 with a siphon pipe is formed from anextraction pipe 75 suspending through and from a mounting bracket 74,and a filtration member 76 fixed to the mounting bracket 74 andsurrounding the extraction pipe 75 in a spaced relationship from theextraction pipe 75 so that a flow path may be formed on the outer sideof the extraction pipe 75. And, the tubular filtration element 62 with asiphon pipe is mounted on a partition plate 73 by fitting or screwingthe mounting bracket 74 into a hole formed in the partition plate 73.Consequently, the top end of the filtration member 76 is closed up withthe mounting bracket 74 while the top end of the extraction pipe 75 isopen in an upper tank (not shown).

For the filtration member 76, a known cylindrical filter made of aceramics material, a porous cylindrical filter made of a sintered metal,a filter of the winding type or a filter of some other suitable type isused. Further, the lower end of the filtration member 76 is closed upintegrally with the same material as the material (a ceramics materialor a sintered metal) from which the side wall of the filtration member76 is formed so that the lower end may have a function as a filter.However, the lower end need not necessarily have a function of a filter,and the lower end of the filtration member 76 may be closed up with amaterial different from the material of the side wall of the filtrationmember 76.

The extraction pipe 75 may be secured to the mounting bracket 74 byfitting or screwing the extraction pipe 75 into the mounting bracket 74or may be formed integrally with the mounting bracket 74. Further, thefiltration member 76 may be secured to the mounting bracket 74 byfitting or securely screwing the filtration member 76 into the lower endof the mounting bracket 74 or may be secured by adhesion.

By employing the tubular filtration element 62 with a siphon pipewherein the extraction pipe 75 is provided on the inner side of thefiltration member 76 in this manner, in the tubular filtration element62 with a siphon pipe, suspension passes through and is filtered by thefiltration member 76. Further, the filtrate filtered by the filtrationmember 76 enters into the extraction pipe 75 from the lower end andreaches the top end of the extraction pipe 75 through a hollow portionof the extraction pipe 75, and is collected into the upper tank.Consequently, upon processing of the suspension in the filtrationequipment, even if the level of the solution becomes lower than thefiltration face of the tubular filtration element 62 with a siphon pipe,until after the level of the solution reaches the lower end of theextraction pipe 75, filtration and recovery by both of the tubularfiltration element 62 with a siphon pipe and the plate filtrationelement (not shown) can be performed, and consequently, the recoveryoperation can be facilitated.

The amount of suspension which can be recovered by such a tubularfiltration element 62 with a siphon pipe as described above depends uponthe position of the lower end of the extraction pipe 75 with respect tothe lower tank. Therefore, in order to recover as much as possible ifthe suspension with the tubular filtration element 62 with a siphonpipe, preferably the lower end of the extraction pipe 75 is extended toa location as near as possible to the lower end of the filtration member76. Further, as regards the length of the filtration member 76, where afiltration collection vessel (not shown) is provided for pivotal motion,it is preferable to make the filtration member 76 as long as possiblewithin a range in which the filtration member 76 does not interfere withthe filtration collection vessel. Where the filtration collection vesselis fixed, the filtration member 76 can be extended in length until thelower end thereof is positioned immediately above the plate filtrationelement.

(Fifth Embodiment)

FIG. 9 is a schematic view of a filtration system in which a fifthembodiment of the filtration equipment of the present invention isemployed.

As shown in FIG. 9, the filtration equipment 81 of the presentembodiment is of the type wherein a filtration element with a siphonpipe is suspended, and includes an upper tank 81a and a lower tank 81bpartitioned and sealed from each other by a partition plate 93. Aplurality of tubular filtration elements 82 having closed up lower endsare suspended on the partition plate 93.

A first delivery pipe 85a for delivering filtrate filtered by thetubular filtration elements 82 to a filtrate storage tank (not shown) isprovided in the upper tank 81a and extends through a side wall of thetank 81a. The first delivery pipe 85a to which a valve 91e is attachedis preferably provided in the proximity of the bottom face of the uppertank 81a, that is, the depth position at which the partition plate isprovided. This is so that as much as possible of the filtrate filteredby the tubular filtration elements 82 and coming to the upper tank 81acan be delivered to the filtrate storage tank. The most preferable formis to provide, in the inside of the partition plate 93, delivery means(solution flow path) interconnecting the top ends of the tubularfiltration elements 82 and the first delivery pipe 85a. Further, a pipeprovided with a valve 91r for the introduction of pressurized gas islocated at a top portion of the tank.

Further, a filtrate collection vessel 83 connected to a second deliverypipe 85b serving as second delivery means via a valve 91k is providedfor pivotal motion at a lower portion of the lower tank 81b. A platefiltration element 84 is mounted on the top face of the filtratecollection vessel 83. A packing is provided over the entirecircumference on an outer peripheral edge of the plate filtrationelement 84, and the airtightness of the space in the inside of the lowertank 81b in which the tubular filtration elements 82 are provided iskept by the packing. This is to prevent suspension supplied into thelower tank 81b from above the plate filtration element 84 from leakingto a location below the plate filtration element 84. Further, adischarging pipe 92 is connected to a line from the filtrate collectionvessel 83 to the valve 91k with a valve 91d interposed therein so thatfiltrate passing through the plate filtration element 84 is dischargedfrom the tank therethrough.

The second delivery pipe 85b joins to an intermediate portion of thefirst delivery pipe 85a, and consequently, the second delivery pipe 85bis connected to the filtrate storage tank via the first delivery pipe85a. A valve 91h is provided on the downstream side of the firstdelivery pipe 85a with respect to the joining portion with the seconddelivery pipe 85b, and a valve 91q is provided for a branching pipe.

An suspension supply pipe 86 is connected to a portion of the lower tank81b above the plate filtration element 84 with a valve 91c interposedtherein. A pump 90 is provided for the suspension supply pipe 86, and bychanging over valves 91a and 91b, suspension stored in an suspensiontank (not shown) or precoat solution stored in a precoat tank 89 issupplied to the tank 81b. The precoat solution contains filter aid to beprecoated on the surfaces of the tubular filtration elements 82 and theplate filtration element 84 prior to filtration of the suspension. Forthe filter aid, diatomaceous earth, perlite, cellulose or some othersubstance is used.

A water introduction pipe 94 serving as pressurized water introductionmeans for introducing pressurized water into the inside of the tank 81bis connected to an upper portion of the tank 81b, and a valve 91m isprovided for the water introduction pipe 94. Further, a gas introductionpipe 87 serving as pressurized gas introduction means for introducingpressurized air or pressurized gas such as carbon dioxide into the tank81b is connected to the tank 81b, and a valve 91f is provided for thegas introduction pipe 87.

A precoating solution feedback pipe 88 is provided to return precoatsolution supplied to the filtration equipment 81 to the precoat tank 89and is connected to the upstream side of the first delivery pipe 85awith respect to the valve 91h, and a valve 91j is provided for theprecoating solution feedback pipe 88.

It is to be noted that, while, for the materials of the tubularfiltration elements 82 and the plate filtration element 84, a filtermade of a porous material such as a ceramics material or a sinteredmetal or a filter of the winding type can be used, since the elementsmay possibly corrode depending upon the properties of the suspension(acid, alkali, high temperature and so forth), an optimum material isused as the material of the elements depending on the properties of thesuspension.

Operation of the filtration system of the present embodiment isdescribed below.

First, precoating processing performed prior to filtration of suspensionis described. Upon precoating, the valves 91b, 91c, 91e, 91k and 91j areopened, and then, the pump 90 is started so that the precoating solutionis circulated from the precoat tank 89 through the suspension supplypipe 86→filtration equipment 81→first delivery pipe 85a, second deliverypipe 85b→precoating solution feedback pipe 88→precoat tank 89.Thereafter, the five valves mentioned above are closed. As a result, aprecoat layer is formed on the surfaces of the tubular filtrationelements 82 and the surface of the plate filtration element 84.

Next, the filtration operation is described. The valves 91a, 91c, 91e,91h and 91k are opened and the pump 90 is rendered operative.Consequently, the suspension in the suspension tank is supplied into thetank 81b through the suspension supply pipe 86 and is filtered by thetubular filtration elements 82 and the plate filtration element 84. Thefiltrate filtered by the tubular filtration elements 82 is delivered tothe filtrate storage tank through the first delivery pipe 85a.Meanwhile, the filtrate filtered by the plate filtration element 84 iscollected into the filtrate collection vessel 83 and delivered to thefiltrate storage tank through the second delivery pipe 85b.

Here, although filtration is performed by the tubular filtrationelements 82 and the plate filtration element 84, it is also possible toclose the valve 91k so that filtration is performed only by the tubularfiltration elements 82. However, unless solution is flowing, duringfiltration, from the primary side (suspension side) to the secondaryside (filtrate side), that is, unless the precoat layers are in acondition pressed against the surfaces of the filtration elements, theprecoat layers are liable to exfoliate, and accordingly, the tubularfiltration elements 82 must always remain in a filtering condition.Further, also the filtration efficiency is improved by performingfiltration with the tubular filtration elements 82 and the platefiltration element 84.

After filtration is perform for a long period of time, filteredsubstances adhere to and are deposited on the surfaces of the tubularfiltration elements 82 and the surface of the plate filtration element84. Since the filtration processing is deteriorated if filteredsubstances are deposited on the surfaces of the tubular filtrationelements 82 and the surface of the plate filtration element 84, thefiltered substances deposited on the tubular filtration elements 82 andthe plate filtration element 84 are removed in accordance withnecessity. Thereupon, the process of recovering the suspension from thefiltration equipment 81 is performed first.

The process of recovering the suspension is described below.

In the process of recoverying suspension, the valves 91e and 91k areopened and the valve 91m of the water introduction pipe 94 is opened tointroduce pressurized water into the tank 81b, and the valve 91c at theexit/entrance for the suspension is closed. Driven by the pressurizedwater, the suspension remaining in the tank 81b is filtered by thetubular filtration elements 82 and the plate filtration element 84 andrecovered into the filtrate storage tank.

As the suspension in the tank 81b decreases as a result of thesuspension recovery processing, the ratio of water to be mixed into thefiltrate increases. Accordingly, the concentration of the filtrate inthe proximity of each of the valves 91e and 91k is monitored by electricconductivity, chromaticity or the like, and when the two suspensionconcentrations exhibit lower concentrations than a fixed level, thevalves 91d and 91q are opened while the valves 91h and 91k are closed,thereby substantially completing the process of recovering thesuspension.

The next step is discharging the pressurized water from the tank. In thecondition described above, the pressurized gas valve 91f at the upperlocation of the suspension side tank is opened to introduce pressurizedgas from the upper location to discharge the pressurized water throughthe upper and lower filtration elements 82 and 84 and the valves 91d and91q. The pressure of the pressurized gas is selected to a suitable valuein accordance with the rate at which the solution in the tank isdischarged.

After the solution in the tank is discharged fully, the condition ismaintained. As a result, water in the filtered substances (calledsludge) adhering to the surfaces of the filters is expelled from thesludge by the pressurized gas and discharged to the outside of the tanktogether with the pressurized gas through the valves 91d and 91q.

Then, the valves 91d, 91f and 91q are closed and the pressurized gasvalve 91r on the filtrate side is opened so that gas is jetted from theinsides of the tubular filtration elements 82 to exfoliate and drop thedeposited sludge. Meanwhile, the adhering sludge and the sludge droppingfrom the tubular filtration elements 82 are deposited on the surface ofthe plate filtration element 84. Also the pressurized gas is dischargedvia the valve 91d.

Since the operation for the removal of the deposited substances on theplate filtration element 84 is similar to that in the second embodiment(FIGS. 2 to 6), description thereof is omitted here.

It is to be noted that, while the sludge in the first to fourthembodiments described above is processed using a cleansing agent anddischarged, discharging the sludge after it is dried as in the presentembodiment rather than discharing it in the form mud is advantageous inthat the succeeding processing can be simplified. From this, also in thefirst to fourth embodiments, the sludge on the surfaces of the filtersmay be exfoliated and removed after it is dried by pressurized gassimilarly as in the fifth embodiment.

While, in the present fifth embodiment, an element with a siphon of thesuspended type is used for the tubular filtration elements, also anordinary tubular filtration element of the upright type is not outsidethe scope of the present invention. However, where an ordinary tubularfiltration element is employed, since the mixture ratio of thepressurized water in the filtrate increases in proportion to the ratioat which the overall surface of the element contacts with thepressurized water, if the allowance for the filtrate is set to a severevalue, then the filtration by the tubular filtration element cannot beperformed for a long time, and the filtration efficiency is deterioratedcomparing with that of the apparatus of the fifth embodiment.

Results of an experiment based on the fifth embodiment are described.

(1) Filtration of Beer

The upper elements of 1,000 mm were used, and when filtration usingdiatomaceous earth was ended at the precoat filtration pressuredifference of 1.0 kgf/cm², filtrate was recovered using CO₂ gas by theconventional method. In this instance, when the gas pressure differencewas set to 10 kgf/cm², the recovery rate was substantially equal to thatupon filtration of beer, but mixture of gas into the filtrate sideoccurred at locations of the upper elements spaced by approximately 300mm from the tops. When the gas pressure difference was 0.5 kgf/cm²,recovery of filtrate was possible without causing mixture of gas untilthe solution level fell to a location in the proximity of the lower endsof the upper elements, but the recovery rate was deteriorated toapproximately one half.

In the present embodiment, in recovery of suspension by the waterpressure of the pressure difference of 1.0 kgf/cm², recovery waspossible while maintaining a recovery rate substantially equal to thatof filtration. Thereafter, the water was discharged, and removal ofsludge by gas purge was performed, which succeeded in exfoliation of thesludge and discharging of the sludge as dry sludge.

(2) Filtration of the Lees of Sake

The upper elements of 1,000 mm was used, and the filtration equipmentwas used for the separation filtration of the lees. In the case of thefinal pressure difference of 5.0 kgf/cm², when filtration recovery wasperformed using air of the pressure difference of 5.0 kgf/cm², mixtureof gas into the filtrate side occurred at locations of the upperelements spaced approximately by 100 mm from the tops. When the pressuredifference was 0.5 kgf/cm², the filtration recovery was stopped atlocations of the upper elements spaced by 50 mm from the tops.

In the case of the present embodiment, in filtrate recovery with thewater pressure of the pressure difference of 5.0 kgf/cm², recovery waspossible while maintaining a filtrate recovery rate substantially equalto that of filtration. Thereafter, the water was discharged, anddischarge of sludge by gas purge was performed, which succeeded inexfoliation of the sludge and discharging of the sludge as dry sludge.

We claim:
 1. A filtration equipment with a filtrate recovery process,which comprises, a tank to which suspension before filtration issupplied, tubular filtration elements provided in said tank forfiltering the suspension, delivery means for delivering the filtratefiltered by said tubular filtration elements to the outside of saidtank, a plate filtration element located below said tubular filtrationelements in the inside of said tank for maintaining the airtightness ofthe space in which said tubular filtration elements are provided, seconddelivery means for delivering the filtrate filtered by said platefiltration element to the outside of said tank, and pressurized gasintroduction means located upstream of the tubular filtration elementsand the plate filtration element for introducing pressurized gas intosaid tank when the suspension in said tank is recovered.
 2. A filtrationequipment with a filtrate recovery process, which comprises, a tank towhich suspension before filtration is supplied, tubular filtrationelements provided in said tank for filtering the suspension, deliverymeans for delivering the filtrate filtered by said tubular filtrationelements to the outside of said tank, a plate filtration element locatedbelow said tubular filtration elements in the inside of said tank formaintaining the airtightness of the space in which said tubularfiltration elements are provided, second delivery means for deliveringthe filtrate filtered by said plate filtration element to the outside ofsaid tank, pressurized liquid introduction means for introducingpressurized liquid into said tank when the suspension in said tank isrecovered, and pressurized gas introduction means located upstream ofthe tubular filtration elements and the plate filtration element forintroducing pressurized gas into said tank in order to discharge theremaining pressurized liquid used for the recovery of the suspensionremaining in said tank to the outside of said tank.
 3. A filtrationequipment as claimed in claim 1 or 2, wherein said tubular filtrationelements and said plate filtration element are fluidically arranged inparallel.
 4. A filtration equipment as claimed in claim any one ofclaims 1 to 2, wherein said plate filtration element is installed sothat it can be inclined with respect to a horizontal plane.
 5. Afiltration equipment as claimed in claim 3, wherein said platefiltration element is installed so that it can be inclined with respectto a horizontal plane.